METAL OBJECT SENSOR, PARTICULARLY FOR RAILWAY WHEELS

• US 3,721,859 A
• Filed: 11/29/1971
• Issued: 03/20/1973
• Est. Priority Date: 12/14/1970
• Status: Expired due to Term

• Current Assignee: ABC Rail Corp.
• Original Assignee: Carl G. Blanyer
• Inventors: Blanyer, Carl G.
• Primary Examiner(s): Hix, L. T.
• Application Number:
  US05/202,755
• Time in Patent Office: 477 Days
• Field of Search: 317/5,DIG.2,146 246/247
• US Class Current: 361/236
• CPC Class Codes: B61L 1/10 actuated by electromagnetic radiation; actuated by particle radiation
• CPC Class Codes: G01P 13/045 with speed indication
• CPC Class Codes: G01P 3/66 using electric or magnetic means G01P3/80 takes precedence; measuring short time intervals G04F8/00, G04F10/00

Abstract

A sensor for sensing movement of a metal object, such as a railway wheel, along a given path, comprising three sensing coils, all tuned to the same operating frequency, spaced along the path with their axes intersecting the path, and connected in series in three consecutive arms of a pentagon bridge. An oscillator, connected to the remaining two bridge arms, excites the coils at their operating frequency. A metal object moving along the path disturbs the fields of the coils in a sequence depending upon its direction of movement; the direction and velocity of the metal object are indicated in output signals derived by additively combining and synchronously detecting the signal voltages developed at the bridge terminals. In the preferred construction, the two end coils each include a few turns encompassing the central coil to reduce mutual coupling between adjacent coils.

Claims

1. A sensor for sensing the passage of a metal object moving along a given path, comprising:

at least three electrical sensing coils, all tuned to a given operating frequency, electrically connected in series with each other in consecutive arms of a bridge Circuit, said sensing coils being positioned in series along said path with their axes parallel to each other and normal to said path;

excitation means, incorporated in two remaining arms of the bridge, for applying an excitation signal, at said operating frequency, in phase opposition to the two end sensing coils of said series so that each sensing coil generates an electromagnetic field intersecting said path;

signal processing means, connected to the bridge terminals intermediate said sensing coils, for additively combining the signals developed at different terminals of said bridge to produce at least two operating signals having amplitude variations indicative of the sequence of disturbance of the fields of said sensing coils by a metal object moving along said path; and

synchronous detector means, coupled to said signal processing means and said excitation means, for demodulating said operating signals to produce at least two output signals indicative of the direction and velocity of said metal object.

2. A metal object sensor according to claim 1, in which said signal processing means includes a first signal combining network for additively combining the excitation signal of one phase in predetermined amplitude ratio with the tap signal developed at one bridge terminal intermediate said sensing coils, and a second signal combining network for additively combining the excitation signal of opposite phase in predetermined ratio with the tap signal developed at another bridge terminal intermediate said sensing coils.

3. A metal object sensor according to claim 2, comprising just three tuned sensing coils connected consecutively to afford, in sequence, a first excitation terminal, a first tap terminal intermediate the first two coils, a second tap terminal intermediate the last two coils, and a second excitation terminal, and in which said first signal combining network is connected to the first excitation terminal and the second tap terminal and said second signal combining network is connected to the second excitation terminal and the first tap terminal.

4. A metal object sensor according to claim 3, in which the combining ratio of excitation signal amplitude to tap signal amplitude, in each combining network, is 1:

3.

5. A metal object sensor according to claim 3, in which said signal processing means further comprises a summing circuit for adding the output signal E3 of said first signal combining network to the output signal E4 of said second signal combining network to develop a first operating signal of the form E3 + E4 comprising two pulses identifying the presence of a metal object over the two end sensing coils, respectively, and a null identifying the presence of a metal object centered over the center sensing coil, the two pulses occurring in reverse order for reversed movement of a metal object past said sensor.

6. A metal object sensor according to claim 5, in which said signal processing means further comprises a difference circuit for subtracting the output signal of one combining network from the output signal of the other to develop a second operating signal of the form E4-E3 comprising a pulse positively identifying the presence of a metal object over the center sensing coil, and having a shape independent of the direction of movement of the metal object along said path.

7. A metal object sensor according to claim 6, in which said second operating signal overlaps both pulses in said first operating signal, for passage of a metal object along said path in either direction.

8. A metal object sensor according to claim 3, in which each end sensing coil includes a compensating winding, wound upon the center coil, each compensating winding including a much smaller number of turns than the main part of the coil, said compensating windings effectively compensating for mutual field coupling between adjacent coils.